Penerapan Model Pembelajaran Atraktif Berbasis Multiple Intelligences Tentang Pemantulan Cahaya pada Cermin

Penelitian ini bertujuan untuk mengetahui efektivitas penerapan model pembelajaran atraktif berbasis multiple intelligences dalam meremediasi miskonsepsi siswa tentang pemantulan cahaya pada cermin. Pada penelitian ini digunakan bentuk pre-eksperimental design dengan rancangan one group pretest-post test design. Alat pengumpulan data berupa tes pilihan ganda dengan reasoning. Hasil validitas sebesar 4,08 dan reliabilitas 0,537. Siswa dibagi menjadi lima kelompok kecerdasan, yaitu kelompok linguistic intelligence, mathematical-logical intelligence, visual-spatial intelligence, bodily-khinestetic intelligence, dan musical intelligence. Siswa membahas konsep fisika sesuai kelompok kecerdasannya dalam bentuk pembuatan pantun-puisi, teka-teki silang, menggambar kreatif, drama, dan mengarang lirik lagu. Efektivitas penerapan model pembelajaran multiple intelligences menggunakan persamaan effect size. Ditemukan bahwa skor effect size masing-masing kelompok berkategori tinggi sebesar 5,76; 3,76; 4,60; 1,70; dan 1,34. Penerapan model pembelajaran atraktif berbasis multiple intelligences efektif dalam meremediasi miskonsepsi siswa. Penelitian ini diharapkan dapat digunakan pada materi fisika dan sekolah lainnya

Size-Dependent Thermal Shifts to MOF Nanocrystal Optical Gaps Induced by Dynamic Bonding

Conventional semiconductor nanocrystals exhibit wide-ranging optical behavior, whereas the size-dependent photophysical properties of metal–organic framework (MOF) nanocrystals remain an open research frontier. Here, we present size- and temperature-dependent optical absorption spectra of common MOFs with particle sizes ranging from tens of nanometers to several micrometers. All materials exhibit optical gaps that decrease at elevated temperatures, which we attribute to the dynamic nature of MOF metal–linker bonds. Accordingly, whereas the labile titanium–carboxylate bonds of MIL-125 give rise to bandgaps that red-shift by ∼600 meV over 300 K, the more rigid zinc–imidazolate bonds of ZIF-8 produce a red-shift of only ∼10 meV. Furthermore, smaller particles induce far larger decreases to optical gaps. Taken together, these results suggest MOF bonding becomes more flexible with smaller nanocrystal sizes, offering a powerful tool for manipulating optical behavior through composition, temperature, and dimensionality

Potentiometric Titrations for Measuring the Capacitance of Colloidal Photodoped ZnO Nanocrystals

Colloidal semiconductor nanocrystals offer a unique opportunity to bridge molecular and bulk semiconductor redox phenomena. Here, potentiometric titration is demonstrated as a method for quantifying the Fermi levels and charging potentials of free-standing colloidal <i>n</i>-type ZnO nanocrystals possessing between 0 and 20 conduction-band electrons per nanocrystal, corresponding to carrier densities between 0 and 1.2 × 10²⁰ cm^–3. Potentiometric titration of colloidal semiconductor nanocrystals has not been described previously, and little precedent exists for analogous potentiometric titration of any soluble reductants involving so many electrons. Linear changes in Fermi level vs charge-carrier density are observed for each ensemble of nanocrystals, with slopes that depend on the nanocrystal size. Analysis indicates that the ensemble nanocrystal capacitance is governed by classical surface electrical double layers, showing no evidence of quantum contributions. Systematic shifts in the Fermi level are also observed with specific changes in the identity of the charge-compensating countercation. As a simple and contactless alternative to more common thin-film-based voltammetric techniques, potentiometric titration offers a powerful new approach for quantifying the redox properties of colloidal semiconductor nanocrystals

NO Disproportionation at a Mononuclear Site-Isolated Fe²⁺ Center in Fe²⁺-MOF‑5

The weak-field ligand environments at the metal nodes of metal–organic frameworks (MOFs) mimic the electronic environment of metalloenzyme active sites, but little is known about the reactivity of MOF nodes toward small molecules of biological relevance. Here, we report that the ferrous ions in Fe²⁺-exchanged MOF-5 disproportionate nitric oxide to produce nitrous oxide and a ferric nitrito complex. Although mechanistic studies of N–N bond forming transformations often invoke a hyponitrite species, as in nitric oxide reductase and NO_<i>x</i> reduction catalysis, little is known about this intermediate in its monoanionic state. Together with the first report of N–N coupling between NO molecules in a MOF, we present evidence for a species that is consistent with a ferric hyponitrite radical, whose isolation is enabled by the spatial constraints of the MOF matrix

Spectroelectrochemical Measurement of Surface Electrostatic Contributions to Colloidal CdSe Nanocrystal Redox Potentials

Understanding and controlling the redox properties of colloidal semiconductor nanocrystals is critical for application of this class of materials in many proposed technologies. Here, we use spectroelectrochemical potentiometry to analyze the redox potentials of free-standing colloidal <i>n</i>-type CdSe nanocrystals. We show that both the redox potentials and the maximum number of conduction-band electrons that can be accumulated through photodoping are strongly affected by the nanocrystal’s surface stoichiometry, varying reproducibly by over 400 meV with changes in relative Cd²⁺:Se^2– surface concentration. The data suggest that Se^2– enrichment generates electric dipoles at the nanocrystal surfaces that shift the CdSe nanocrystal band-edge potentials to more negative values, and these generated dipoles are largely eliminated upon Cd²⁺ binding. These results demonstrate the importance of nanocrystal surface stoichiometry in applications involving tuned nanocrystal redox potentials, band-edge alignment, or electron-transfer driving forces

Degenerately <i>n</i>‑Doped Colloidal PbSe Quantum Dots: Band Assignments and Electrostatic Effects

We present a spectroscopic study of colloidal PbSe quantum dots (QDs) that have been photodoped to introduce excess delocalized conduction-band (CB) electrons. High-quality absorption spectra are obtained for these degenerately doped QDs with excess electron concentrations up to ∼10²⁰ cm^–3. At the highest doping levels, electrons have completely filled the 1S_e orbitals of the CB and partially populated the higher-energy 1P_e orbitals. Spectroscopic changes observed as a function of carrier concentration permit an unambiguous assignment of the second excitonic absorption maximum to 1P_h-1P_e transitions. At intermediate doping levels, a clear absorption feature appears between the first two excitonic maxima that is attributable to parity-forbidden 1S_h,e-1P_e,h excitations, which become observable because of electrostatic symmetry breaking. Redshifts of the main excitonic absorption features with increased carrier concentration are also analyzed. The Coulomb stabilization energies of both the 1S_h-1S_e and 1P_h-1P_e excitons in <i>n</i>-doped PbSe QDs are remarkably similar to those observed for multiexcitons with the same electron count. The origins of these redshifts are discussed

Copper-Coupled Electron Transfer in Colloidal Plasmonic Copper-Sulfide Nanocrystals Probed by <i>in Situ</i> Spectroelectrochemistry

Copper-sulfide nanocrystals can accommodate considerable densities of delocalized valence-band holes, introducing localized surface plasmon resonances (LSPRs) attractive for infrared plasmonic applications. Chemical control over nanocrystal shape, composition, and charge-carrier densities further broadens their scope of potential properties and applications. Although a great deal of control over LSPRs in these materials has been demonstrated, structural complexities have inhibited detailed descriptions of the microscopic chemical processes that transform them from nearly intrinsic to degenerately doped semiconductors. A comprehensive understanding of these transformations will facilitate use of these materials in emerging technologies. Here, we apply spectroelectrochemical potentiometry as a quantitative <i>in situ</i> probe of copper-sulfide nanocrystal Fermi-level energies (<i>E</i>_F) during redox reactions that switch their LSPR bands on and off. We demonstrate spectroscopically indistinguishable LSPR bands in low-chalcocite copper-sulfide nanocrystals with and without lattice cation vacancies and show that cation vacancies are much more effective than surface anions at stabilizing excess free carriers. The appearance of the LSPR band, the shift in <i>E</i>_F, and the change in crystal structure upon nanocrystal oxidation are all fully reversible upon addition of outer-sphere reductants. These measurements further allow quantitative comparison of the coupled and stepwise oxidation/cation-vacancy-formation reactions associated with LSPRs in copper-sulfide nanocrystals, highlighting fundamental thermodynamic considerations relevant to technologies that rely on reversible or low-driving-force plasmon generation in semiconductor nanostructures

Microscopy of leaves from different Bergenia species.

Plants of the genus Bergenia are part of remedies used in Ayurveda medicine. They also play an important part in traditional healing practice in China, India, Mongolia and Russia. Theoretical part of this thesis sums the newest findings and research results concerning three Bergenia species: Bergenia ciliata (Haw.) Sternb., Bergenia crassifolia (L.) Fritsch a Bergenia ornata Stein. The thesis mainly focuses on their current and potential use in medicine and pharmacy. Bergenia extract is traditionally used for dissolving kidney stones, treating respiratory tract illnesses and to stop bleeding. The most important active substances of these plants, their characteristics and main effects are also noted. Bergenia is an important source of arbutin and bergenin. Bergenin has antitussive, antiflogistic and gastroprotective effects. Arbutin is used to treat urinary tract diseases and in cosmetology to lighten the skin. The experimental part of this thesis includes methods of preparation of permanent microscope slides from leaves of chosen Bergenia species. Photographs have been taken from both permanent and native slides. Anatomy of the leaf and leaf epidermis is described including stomatal index. Presence of calcium oxalate crystals in form of druses is also documented. Basic anatomical features were..

Potentiometric Measurements of Semiconductor Nanocrystal Redox Potentials

A potentiometric method for measuring redox potentials of colloidal semiconductor nanocrystals (NCs) is described. Fermi levels of colloidal ZnO NCs are measured <i>in situ</i> during photodoping, allowing correlation of NC redox potentials and reduction levels. Excellent agreement is found between electrochemical and optical redox-indicator methods. Potentiometry is also reported for colloidal CdSe NCs, which show more negative conduction-band-edge potentials than in ZnO. This difference is highlighted by spontaneous electron transfer from reduced CdSe NCs to ZnO NCs in solution, with potentiometry providing a measure of the inter-NC electron-transfer driving force. Future applications of NC potentiometry are briefly discussed

Ligand Redox Non-innocence in the Stoichiometric Oxidation of Mn₂(2,5-dioxidoterephthalate) (Mn-MOF-74)

Unsaturated metal sites within the nodes of metal–organic frameworks (MOFs) can be interrogated by redox reagents common to small molecule chemistry. We show, for the first time, that an analogue of the iconic M₂(2,5-dioxidoterephthalate) (M₂DOBDC, MOF-74) class of materials can be stoichiometrically oxidized by one electron per metal center. The reaction of Mn₂DOBDC with C₆H₅ICl₂ produces the oxidized material Cl₂Mn₂DOBDC, which retains crystallinity and porosity. Surprisingly, magnetic measurements, X-ray absorption, and infrared spectroscopic data indicate that the Mn ions maintain a formal oxidation state of +2, suggesting instead the oxidation of the DOBDC^4– ligand to the quinone DOBDC^2–. These results describe the first example of ligand redox non-innocence in a MOF and a rare instance of stoichiometric electron transfer involving the metal nodes. The methods described herein offer a synthetic toolkit that will be of general use for further explorations of the redox reactivity of MOF nodes